The invention relates to a valve lift control device, which controls a valve lift according to operating conditions of an internal combustion engine such as an engine when an intake valve or an exhaust valve of the engine is opened and closed due to a cam via a tappet.
Generally, with a valve operating system of the internal combustion engine, both of the valve lift and an angular aperture are reduce during a low-rpm condition. In this way, the velocity of a mixed gas is increased to improve combustion efficiency. On the other hand, both of the valve lift and an overlap are increased during a high-rpm condition to improve a suction efficiency through the use of an exhaust inertial effect. In this way, it results in enhancement of fuel economy and improvement of power of the internal combustion engines.
With the valve operating system as discussed above, the valve lift control device used in conjunction with a valve timing control device is disclosed in JP-A-1998/507242, for example.
The valve lift control device includes a plurality of cams arranged on a camshaft being driven rotationally in synchronization with a rotation of an internal combustion engine, an inner tappet movable reciprocally in an axial direction of a valve rod pursuant to a cam profile of a low-lift cam pertinent to the opening and the closing of the valve during a low-rpm condition (equivalent of a low-lift mode) of the above cams, an outer tappet arranged outside of the inner tappet and movable reciprocally in an axial direction of a valve rod pursuant to a cam profile of a high-lift cam pertinent to the opening and the closing of the valve during a high-rpm condition (equivalent of a high-lift mode), and a movable member arranged in the inner tappet and movable in a radial direction of the inner tappet.
The movable member is moved outwardly in a radial direction of the inner tappet due to a hydraulic pressure, which is supplied to a central section of the inner tappet in the high-lift mode, to engage whith a recess formed at an inner peripheral section of the outer tappet. As a result, both tappets are integrated. The hydraulic pressure is reduced in the low-lift mode, and the movable member is moved inwardly in the radial direction of the inner tappet due to a biasing means such as spring and so on to be disconnected from the recess of the outer tappet. As a result, both tappets are separated.
With the conventional valve lift control device, a hydraulic pressure necessary to engage the movable member with the recess of the outer tappet must be however supplied to the central section of the inner tappet. The hydraulic system is complicated in construction, and causes a disturbance of operation.
Moreover, JP-A-1998/141030 discloses the same technical information as the gazette described above.
The invention was made to solve the foregoing problems, and an object of the invention is to provide a valve lift control device having a simple structure to ensure good operating reliability.
A valve lift control device according to the invention comprises an inner tappet biased toward a low-lift cam pertinent to the opening and the closing of a valve in the low-lift mode acting as one of cams which are arranged on a camshaft being driven rotationally in synchronization with a rotation of an internal combustion engine; an outer tappet arranged outside of the inner tappet and biased toward a high-lift cam pertinent to the opening and the closing of the valve in the high-lift mode among the plurality of cams; and a rotational member being arranged rotationally in a peripheral direction of the inner and outer tappets and including at least one projection member being outwardly projected from a perimeter of the inner tappet and an engagement section engaging with the projection member, characterized in that a relative sliding of the inner and outer tappets in an axial direction of the tappet is blocked or allowed due to a rotation of the rotational member in a required range. In this way, the valve lift control device is simply constituted as compared with the conventional valve lift control device, and facilitates selection between a valve lift during a low-rpm condition and a valve lift during a high-rpm condition. It is therefore possible to ensure good operating reliability and good stability in each parts of the device.
With the above arrangement, the valve lift control device is characterized in that the projection member is a rod-shaped member projected from the outer periphery of the inner tappet. In this way, since the rod-shaped member acting as the projection member is projected from the outer periphery of the inner tappet, it is possible to ensure that the rod-shaped member is engaged with and disengaged from an engagement section of the rotational member.
With the above arrangement, the valve lift control device is characterized in that the rod-shaped member passes through the interior of the inner tappet in a radial direction, and that at least one end of the rod-shaped member is projected outwardly from the perimeter of the inner tappet in the radial direction. In this way, since the rod-shaped member acting as the projection member is projected outwardly from the outer periphery of the inner tappet in the radial direction, it is possible to ensure that the rod-shaped member is engaged with and disengaged from an engagement section of the rotational member.
With the above arrangement, the valve lift control device is characterized in that the rotational member is movable in one direction in two peripheral directions of the inner and outer tappets, respectively, due to a hydraulic pressure. In this way, it is possible to ensure moving smoothly the rotational member to lock the rod-shaped member.
With the above arrangement, the valve lift control device is characterized in that the rotational member is movable in the other direction in two peripheral directions of the inner and outer tappets, respectively, due to a mechanical biasing force. In this way, it is possible to ensure moving smoothly the rotational member to release a lock of the rod-shaped member.
With the above arrangement, the valve lift control device is characterized in that the rotational member is movable in both peripheral directions of the inner and outer tappets, respectively, due to a hydraulic pressure. In this way, it is possible to ensure moving smoothly the rotational member to perform a lock of the rod-shaped member and the release the lock.
With the above arrangement, the valve lift control device is characterized in that the rotational member has a recess, which is engaged with the projection member. In this way, when the lock of the projection member is released due to the rotational member, it is possible to ensure the relative sliding of the inner and outer tappets in an axial direction of the tappet within a stroke.
With the above arrangement, the valve lift control device is characterized in that the projection has a plane face acting as a contact face, which comes into contact with the rotational member. In this way, the rotational member can come into contact with the projection member with stability.
With the above arrangement, the valve lift control device is characterized in that at least one end of the projection member is projected outwardly from the outer periphery of the inner tappet in a radial direction, and is engaged with a groove formed at an inner face of a cylindrical aperture, which supports slidably the outer tappet, of a cylinder head in a sliding direction. In this way, it is possible to control a free rotation of the inner and outer tappets.
With the above arrangement, the valve lift control device is characterized in that an edge of a contact face, which comes into contact with the low-lift cam, of the inner tappet is arranged outside of an orbit of a cam profile of the low-lift cam, apart from the low-lift cam. In this way, since the low-lift cam is kept from contact with the edge of the contact face, which comes into contact with the low-lift cam, of the inner tappet, it is possible to ensure a smooth sliding of the low-lift cam with respect to the inner tappet.
With the above arrangement, the valve lift control device is characterized in that the rotational member has the shape of a sector, at least one thereof is arranged in a holder having a bobbin-shape, and is held rotationally in peripheral directions of the rotational member. In this way, since the rotational member having the shape of a sector can be rotated easily within the holder, it is possible to ensure a good hydraulic response.
With the above arrangement, the valve lift control device is characterized in that a stopper controlling a range allowing rotation of the rotational member is arranged at a portion of a groove of the bobbin-shaped holder. In this way, since the stopper controls the range allowing rotation of the rotational member, it is possible to control the relative sliding of the inner and outer tappets in the axial direction of the tappet with reliability.
With the above arrangement, the valve lift control device is characterized in that a torsion-spring, which biases the rotational member in one direction of peripheral directions of the inner and outer tappets, is provided. Thus, when rotation of the rotational member is performed due to a hydraulic pressure, and the hydraulic pressure is not supplied under abnormal conditions, the rotational member can be rotated due to a mechanical biasing force of the torsion-spring in a safety direction ensuring a relative position of the tappets.
With the above arrangement, the valve lift control device is characterized in that the inner tappet is provided with a slide-bearing member having a contact face, which comes into contact with the low-lift cam, of the inner tappet and allowing mating with and de-mating from the inner tappet. In this way, it is possible to ensure a smooth sliding of the low-lift cam with respect to the inner tappet.
With the above arrangement, the valve lift control device is characterized in that a rotational location control means is provided, controlling a relative rotational location between the slide-bearing member and the inner tappet. In this way, it is possible to prevent the inner tappet from a malfunction, which causes by the high-lift cam when the slide-bearing member differ from a standard to cross the orbit of the high-lift cam.
With the above arrangement, the valve lift control device is characterized in that the slide-bearing member covers with a portion of the outer tappet apart from a contact face, which comes into contact with the high-lift cam, of the outer tappet. In this way, it is possible to ensure a smooth sliding of the low-lift cam with respect to the inner tappet and a smooth sliding of the high-lift cam with respect to the outer tappet.
With the above arrangement, the valve lift control device is characterized in that the slide-bearing member is accommodated in a groove formed at a portion of the outer tappet apart from a contact face, which comes into contact with the high-lift cam, of the outer tappet, wherein a contact face of the slide-bearing member is flush with the contact face of the outer tappet. In this way, a base circle diameter of the high-lift cam can be identical to that of the low-lift cam, the cams being arranged on a camshaft.
A valve lift control device according to the invention comprises an inner tappet biased toward a low-lift cam pertinent to the opening and the closing of a valve in the low-lift mode acting as one of cams which are arranged on a camshaft being driven rotationally in synchronization with a rotation of an internal combustion engine; an outer tappet arranged outside of the inner tappet and biased toward a high-lift cam pertinent to the opening and the closing of the valve in the high-lift mode among the plurality of cams; a rod-shaped member allowing the relative sliding between the inner and outer tappets in an axial direction of the tappet within a stroke equivalent to a difference between a valve lift due to the low-lift cam and a valve lift due to the high-lift cam; a rotational member moving in one direction of peripheral directions of the inner and outer tappets to lock the rod-shaped member and accordingly to move integrally the inner and outer tappets in the axial direction thereof; and a hydraulic mechanism arranged outside of the inner tappet to allow the lock and release of the rod-shaped member due to the rotational member. In this way, it is not necessary to supply the hydraulic pressure to the internal of the inner tappet. Since the device can be simply constituted, it is possible to ensure good operating reliability and good stability in each parts of the device.